1. Field of the Invention
The present invention relates to an inverting apparatus and, more particularly, to an inverting apparatus suitable for use in speed control of an induction motor.
2. Description of the Prior Art
Hitherto, inverting apparatuses are used to variably control the speed of the induction motor.
Namely, the induction motor to drive the compressor for compressing the refrigerant is directly driven at the output frequency of a commercially available power source when the refrigerating performance is low. When a high refrigerating performance is required, the output frequency of the commercially available power source is converted to a frequency higher than this output frequency by an inverting apparatus and the induction motor is driven at this high frequency. As an apparatus regarding such a conventional speed control of the motor, the apparatus disclosed in, for example, Japanese Patent Laid-Open No. 108645/85 is known.
However, in such a conventional speed control of the motor, when the operation by the commercially available power source and the operation at a variable frequency are together used, there is a disadvantage that the power sources of two systems must be prepared, respectively.
There is also a drawback that the apparatus becomes complicated since the power sources of two systems are used.